1. Field of the Invention
The present invention relates to prosthetic joints in general and, in particular, to controllable braking systems for prosthetic knee joints.
2. Description of the Related Art
Three types of variable-torque brakes have been employed in prosthetic knees in the past: (i) dry friction brakes where one material surface rubs against another surface with variable force; (ii) viscous torque brakes using hydraulic fluid squeezed through a variable sized orifice or flow restriction plate; and (iii) magnetorheological (MR) brakes or dampers where MR fluid (containing small iron particles suspended in the fluid) is squeezed through a fixed orifice or flow restriction plate, with viscosity of the fluid being varied in response to an applied magnetic field. Each of these technologies, as conventionally practiced in the field of prosthetics, can pose certain disadvantages.
Though dry friction brakes can generally provide a substantial torque range for their size, undesirably, they are often difficult to control. After extended use, the frictional pads tend to wear, thereby changing the frictional characteristics of the brake and the torque response for a given commanded torque. Disadvantageously, this can cause unreliable damping performance, and hence adversely affect the gait of the amputee and also cause discomfort to the amputee. Consequently, dry friction brakes may need frequent servicing and/or replacement which undesirably adds to the cost.
Under high loading conditions, viscous torque brakes are susceptible to leakage of hydraulic fluid and possibly other damage due to excessive pressure build-up. Disadvantageously, this can result in an irreversible state, since once the brake unit is overloaded it cannot return to normal. Therefore, such a viscous torque brake for a prosthetic joint is prone to catastrophic failure, and hence can be unreliable and detrimental to the safety of an amputee.
The term xe2x80x9cvalve modexe2x80x9d refers to the control of the flow of a MR fluid through an orifice by the application of a variable magnetic field perpendicular to the direction of the flow in place of the mechanical valve used in conventional viscous torque brakes.
Disadvantageously, a MR brake operated in the xe2x80x9cvalve modexe2x80x9d also develops internal fluid pressure buildup, and hence is still susceptible to traditional pressure-induced failure, thereby putting the amputee at risk.
Accordingly it is one important advantage of the present invention to overcome some or all of the above limitations by providing a variable-torque magnetorheologically actuated prosthetic knee which utilizes a plurality of interspersed and alternating rotors and stators to shear magnetorheological fluid in gaps formed therebetween. Advantageously, by operating in the xe2x80x9cshear modexe2x80x9d there is substantially no or negligible fluid pressure buildup or change. Moreover, the multiple MR fluid gaps or flux interfaces desirably allow for the production of a large torque at low speedxe2x80x94eliminating the need for a transmissionxe2x80x94and also for a wide dynamic torque range. One embodiment of the invention allows the rotors and/or stators to close the gaps therebetween to create a frictional torque component, thereby forming a xe2x80x9chybridxe2x80x9d braking system which provides a total torque or damping which is a combination of viscous torque and frictional torque.
In accordance with one preferred embodiment, a magnetorheologically actuated rotary prosthetic knee is provided for precisely and rapidly controlling lower limb movement. The prosthetic knee generally comprises a substantially central core and a pair of side plates, a plurality of interspersed and alternating magnetically soft rotors and magnetically soft stators, an electromagnet positioned between the core and the rotors and stators, and a pair of bearings. The core and the side plates are formed from a magnetically soft material to create a magnetic return path. The rotors and stators are arranged so as to form a plurality of gaps therebetween. The gaps contain a magnetorheological fluid which is sheared during knee rotation. The electromagnet is responsive to an electrical signal to generate a variable magnetic field to cause a controlled change in the viscosity of the magnetorheological fluid. The bearings are in rotary communication with the rotors and a shin portion of the lower limb to transfer rotary resistive torques from the prosthetic knee to the shin portion.
In accordance with another preferred embodiment, a controllable magnetorheological brake for an artificial knee is provided to dampen knee joint rotation. The magnetorheological knee generally comprises a plurality of alternatingly arranged and spaced magnetizable rotors and magnetizable stators, a magnetorheological fluid, and a magnet. The rotors and stators are concentrically configured about a longitudinal axis of rotation of the artificial knee. The magnetorheological fluid resides in a plurality of gaps formed between the rotors and the stators. The magnet is responsive to an applied voltage and adapted to generate a variable magnetic field which passes through the rotors, the stators and the magnetorheological fluid. The shearing of the magnetorheological fluid in the gaps between the rotors and the stators creates a variable torque output which precisely controls the rotation of the artificial knee.
In accordance with yet another preferred embodiment, an electronically controlled prosthetic knee is provided for generating a wide dynamic torque range. The prosthetic knee generally comprises a plurality of rotors, a plurality of stators, and a fluid adapted to undergo a rheology change in response to an applied magnetic field. The rotors comprise a ferrous material. The rotors are rotatable and laterally displaceable about a longitudinal axis of rotation of the prosthetic knee. The stators comprise a ferrous material and are alternatingly interspersed with the rotors to form gaps therebetween. The stators are laterally displaceable about the axis of rotation of the prosthetic knee. The fluid resides in the gaps formed between the rotors and the stators. Actuation of the magnetic field generates during knee rotation a controllable variable knee damping torque.
In accordance with a further preferred embodiment, a rotary prosthetic knee for an amputee is provided. The prosthetic knee generally comprises a rotatable inner spline, a plurality of rotors engaged with the inner spline, a plurality of stators alternatingly interspersed with the rotors, an outer spline engaged with the stators, and a magnetically controlled medium residing in a plurality of sealed gaps between the rotors and the stators. The magnetically controlled medium is adapted to undergo a controlled bulk property change in response to an applied magnetic field such that the rotation of the rotors which shear the magnetically controlled medium is precisely controlled and the rotation of the prosthetic knee is variably damped to provide a substantially natural gait for the amputee.
In accordance with one preferred embodiment, a variable torque magnetorheological brake for a prosthetic knee is provided. The brake generally comprises a substantially central core, a first side plate connected to a first end of the core, a second side plate connected to a second end of the core and a rotatable and laterally displaceable blade positioned between the first side plate and the second side plate. The brake further comprises magnetorheological fluid in a pair of microgaps formed between the blade and the plates, and a magnet to generate a magnetic field such that a magnetic circuit is created through the core, the first side plate, the second side plate, the blade and the magnetorheological fluid. The microgaps have a size which is optimally minimized such that when the magnetic field has a zero value there is substantially no frictional contact between the blade and the side plates, thereby allowing the prosthetic knee to swing freely and provide a wide dynamic range.
In accordance with another preferred embodiment, a controllable rotary damper for an artificial knee is provided. The damper generally comprises a plurality of interspersed inner rotors and outer rotors, a plurality of magnetorheological fluid films, a pair of side plates and an electromagnet. The inner rotors and outer rotors are concentrically arranged about a longitudinal axis of the artificial knee. The magnetorheological fluid films are resident in a plurality of gaps between the inner rotors and the outer rotors. The pair of side plates sandwiches the inner rotors and the outer rotors with at least one of the side plates being laterally movable along the longitudinal axis of the artificial knee. The electromagnet is adapted to create a magnetic field through the inner rotors, the outer rotors, the magnetorheological fluid and the side plates. The relative rotation between the inner rotors and the outer rotors and the lateral movement of at least one of the side plates generates a variable damping torque to control the rotation of the artificial knee.
In accordance with one preferred embodiment, a prosthetic knee is provided. The prosthetic knee generally comprises a plurality of rotors, a plurality of stators and a fluid adapted to undergo a rheology change in response to an applied magnetic field. The rotors are rotatable about a longitudinal axis of the prosthetic knee. The stators are alternating interspersed with the rotors to form gaps therebetween. The fluid resides in the gaps formed between the rotors and the stators. Controlled variation of the magnetic field varies the fluid rheology and shearing of the fluid caused by relative rotation between the rotors and stators during knee rotation generates a controllable variable knee torque.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.